Síntese de nanopartículas de ouro e prata em óleo de mamona para a obtenção de espectros SERS de agrotóxicos

Abstract

SERS substrates based on thin films from metallic gold and silver nanoparticles dispersed in castor oil were used for the characterization of the adsorption of pesticide molecules. The adsorption on the gold and silver metallic surfaces of three pesticides was analyzed: 2,4-D, Diuron and Tebuconazole. The thin films obtained from the plasmonic Au and Ag nanoparticles dispersed in castor oil allow the identification of the adsorption of pesticide molecules by surface enhanced Raman scattering (SERS) spectroscopy which technique has the capability of detecting molecules in concentrations of approximately parts per million units, when compared with the conventional Raman spectroscopy technique. The band assignments for the pesticides 2,4-D, Diuron and Tebuconazole were made by the analysis of the recorded SERS spectra. It was possible to verify that the molecular site involved in the adsorption of the 2,4-D pesticide on the metallic surface is the carboxylate group, with the phenyl ring close to a position perpendicular to its surface. The assignment to Diuron's SERS spectrum allowed us to infer that the two nitrogen groups present in the molecules are the sites of interaction with the surface of gold nanoparticle. On the other hand, for the Tebuconazole pesticide the intensification of SERS bands attributed to the normal modes of the triazole group, allows to affirm the interaction with the metal surface occurs by this functional group. The study of the interactions of pesticide molecules with the metallic nanoparticles in different substrates allowed the determination of the most favorable conditions for the occurrence of adsorption. Therefore, the thin film obtained by the dissolution of the analites in the suspension used for the deposition of the nanoparticles was the most suitable medium for obtaining the SERS spectra of the pesticides indicating that the solubility in the hydrophobic medium favored adsorption on the metal surface. The hydroxyl groups, present in the structure of the castor oil triacylglycerol, proved to be effective agents in the formation and stabilization of the synthesized metallic nanoparticles and favored the interaction of pesticide molecules in experiments with thin films.